The invention relates to the general field of optical lithography with particular reference to anti-reflection coatings.
As the feature size of semiconductor devices decreases, critical dimension (CD) control becomes an important task. The xe2x80x9cswing effectxe2x80x9d (line width variation due to wafer surface topography and resist thickness variation) needs to be minimized during lithograph processes. There are at least two ways to reduce this undesired swing effect.
1. A bottom anti-reflective coating (BARC), applied at the interface between the photoresist and the highly reflective substrate, has been very effective in reducing line width varaitions. A popular BARC method is to spin coat a relatively thick organic film to absorb light reflected from the substrate. This is illustrated in FIG. 1 where organic BARC 15 has been inserted between the upper surface of substrate 11 and photoresist layer 61. Incoming light ray 62 is partially reflected as 63 while the rest continues into BARC 15 as ray 17 which is rapidly absorbed by 15 so that the amount of reflected light 18, from the surface of 11, is greatly reduced. Also, as fringe benefit, organic ARCs have a planarizing effect, as shown by the non-conformal coverage of step 21 (typically a metallic line).
2. Use of chemical vapor deposition (CVD) deposited dielectric anti-reflective coating (DARC) layers. At present, DARC layer deposition by CVD is one of the major approaches for deep ultraviolet (DUV) lithography. The primary advantage of a CVD-deposited dielectric film is that its optical properties are directly related to its film stochiometry composition (such as Si, O, N, C ) which can be precisely tuned by adjusting the CVD process parameters: gas ratio, pressure, power, spacing . . . etc. This is illustrated in FIG. 2 where incoming light ray 62, after traversing photoresist layer 61, is reflected from both the top and bottom surfaces of DARC 12 as rays 64 and 65, respectively. Through control of the refractive index and thickness of DARC 12, rays 64 and 65 can be set to be 180xc2x0 out of phase so that destructive interference occurs and no light gets reflected from the bottom surface of the photoresist.
The present invention offer a key advantagexe2x80x94improved control of RI and K for the same DARC thickness.
A routine search of the prior art was performed with the following references of interest being found:
In U.S. Pat. No. 6,291,363 B1, Yin et al. show an ammonia based treatment of a dielectric anti-reflective coating (DARC) layer to minimize formation of defects therein. U.S. Pat. No. 6,228,760 B1 (Lee et al.) shows a SION or SIOX DARC layer process while in U.S. Pat. No. 6,063,704 Demirliogiu discloses a silicon oxynitride dielectric anti-reflective coating layer process wherein a DARC is given added silicon so that it can be used in a SALICIDE process. In U.S. Pat. No. 6,060,132, Lee discloses a chemical vapor deposition dielectric anti reflective coating layer process and uses a plasma treatment to remove contamination by a resist.
It has been an object of at least one embodiment of the present invention to provide a dielectric anti-reflection coating having predetermined optical properties.
Another object of at least one embodiment of the present invention has been that said optical properties include refractive index and extinction coefficient.
Still another object of at least one embodiment of the present invention has been to provide a process for manufacturing said coating.
A further object of at least one embodiment of the present invention has been to provide means for controlling said process in order to obtain optimum results.
These objects have been achieved by depositing said dielectric anti-reflection coating as a series of sub-coatings. After each sub-coating has been deposited it is subjected to surface treatment through exposure to a gaseous plasma. Generally the finished film will comprise 3-5 of these sub-coatings. Software simulation is used to determine the precise composition of each sub-layer as well as its optical properties. In-situ or off-line measurement of each sub-layer can also be used as a tool to guide conditions for deposition of the next sub-layer.